The intersection of capsule gene expression, hypermucoviscosity and hypervirulence in Klebsiella pneumoniae

Heptavalent O-Antigen Bioconjugate Vaccine Exhibiting Differential Functional Antibody Responses Against Diverse Klebsiella pneumoniae Isolates

Klebsiella pneumoniae is the leading cause of neonatal sepsis and is increasingly difficult to treat owing to antibiotic resistance. Vaccination represents a tractable approach to combat this resistant bacterium; however, there is currently not a licensed vaccine. Surface polysaccharides, including O-antigens of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting 7 predominant O-antigen subtypes in K. pneumoniae. Each bioconjugate was immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains. Furthermore, serum from vaccinated mice induced complement-mediated killing of many of these strains. Finally, increased capsule interfered with the ability of O-antigen antibodies to bind and mediate killing of some K. pneumoniae strains. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits limited efficacy against some, but not all, K. pneumoniae isolates.

RfaH contributes to maximal colonization and full virulence of hypervirulent Klebsiella pneumoniae

Hypervirulent K. pneumoniae (hvKp) have emerged as clinically important pathogens, posing a serious threat to human health. RfaH, a transcriptional elongation factor, has been regarded as implicated in facilitating the transcription of long virulence operons in certain bacterial species. In K. pneumoniae, RfaH plays a vital role in promoting CPS synthesis and hypermucoviscosity, as well as mediating bacterial fitness during lung infection. In this study, we aim to conduct a systematic investigation of the roles of rfaH in the survival, dissemination, and colonization of hvKp through in vitro and in vivo assays. We found that bacterial cells and colonies displayed capsule -deficient phenotypes subsequent to the deletion of rfaH in K. pneumoniae NTUH-K2044. We confirmed that rfaH is required for the synthesis of capsule and lipopolysaccharide (LPS) by positively regulating the expression of CPS and LPS gene clusters. We found that the ΔrfaH mutant led to a significantly decreased mortality of K. pneumoniae in a mouse intraperitoneal infection model. We further demonstrated that the absence of rfaH was associated with slower bacterial growth under conditions of low nutrition or iron limitation. ΔrfaH displayed reduced survival rates in the presence of human serum. Besides, the engulfment of the ΔrfaH mutant was significantly higher than that of NTUH-K2044 by macrophages in vivo, indicating an indispensable role of RfaH in the phagocytosis resistance of hvKp in mice. Both mouse intranasal and intraperitoneal infection models revealed a higher bacterial clearance rate of ΔrfaH in lungs, livers, and spleens of mice compared to its wild type, suggesting an important role of RfaH in the bacterial survival, dissemination, and colonization of hvKp in vivo. Histopathological results supported that RfaH contributes to the pathogenicity of hvKp in mice. In conclusion, our study demonstrates crucial roles of RfaH in the survival, colonization and full virulence of hvKp, which provides several implications for the development of RfaH as an antibacterial target.

Hypervirulent Klebsiella pneumoniae with a hypermucoviscosity phenotype challenges strategies of water disinfection for its capsular polysaccharides

Due to the strong pathogenicity of hypervirulent Klebsiella pneumoniae (hvKP), its performance against disinfectants in water should be understood to protect public health and ecological environment. Unfortunately, the disinfectant tolerance of hvKP with a hypermucoviscosity (HMV) phenotype is a critical underexplored area. Here, the tolerance of K. pneumoniae isolates to common disinfectants was evaluated, and its underlying mechanisms were clarified. Results showed that hvKP strains with HMV exhibited remarkable tolerance to triclosan (TCS), sodium hypochlorite (NaClO), and benzalkonium bromide (BB), surpassing that of low-virulent K. pneumoniae (lvKP) and Escherichia coli, which is the microbial indicator of drinking water quality. Ct value of NaClO reached 4.41 mg/L·min to kill 4-log hvKP, while the values were 2.52 and 2.28 mg/L·min to achieve 4-log killing of lvKP and E. coli, respectively. The curing of the virulence plasmid from hvKP strain K2044 revealed that capsular polysaccharide (CPS) synthesis, driven by the virulence plasmids, helped mitigate cell membrane injury and bacterial inactivation under NaClO stress; consequently, it provided a protective advantage to hvKP. Enhancing the antioxidative stress system to reduce ROS production and mitigate oxidative stress caused by NaClO further improved the disinfectant resistance of hvKP strains with HMV. This study emphasized that hvKP strains with HMV posed a considerable challenge to disinfection procedure of water treatment. It also revealed that an improved dosage of NaClO ensures bacteria killing, indicating the optimization of the design of water treatment processes involving disinfection strategies and technical parameters should be considered.

Clinical and laboratory insights into the threat of hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) typically causes severe invasive infections affecting multiple sites in healthy individuals. In the past, hvKP was characterized by a hypermucoviscosity phenotype, susceptibility to antimicrobial agents, and its tendency to cause invasive infections in healthy individuals within the community. However, there has been an alarming increase in reports of multidrug-resistant hvKP, particularly carbapenem-resistant strains, causing nosocomial infections in critically ill or immunocompromised patients. This presents a significant challenge for clinical treatment. Early identification of hvKP is crucial for timely infection control. Notably, identifying hvKP has become confusing due to its prevalence in nosocomial settings and the limited predictive specificity of the hypermucoviscosity phenotype. Novel virulence predictors for hvKP have been discovered through animal models or machine learning algorithms, while standardization of identification criteria is still necessary. Timely source control and antibiotic therapy have been widely employed for the treatment of hvKP infections. Additionally, phage therapy is a promising alternative approach due to escalating antibiotic resistance. In summary, this narrative review highlights the latest research progress in the development, virulence factors, identification, epidemiology of hvKP, and treatment options available for hvKP infection.

RNA interactome of hypervirulent Klebsiella pneumoniae reveals a small RNA inhibitor of capsular mucoviscosity and virulence

Hypervirulent Klebsiella pneumoniae (HvKP) is an emerging bacterial pathogen causing invasive infection in immune-competent humans. The hypervirulence is strongly linked to the overproduction of hypermucoviscous capsule, but the underlying regulatory mechanisms of hypermucoviscosity (HMV) have been elusive, especially at the post-transcriptional level mediated by small noncoding RNAs (sRNAs). Using a recently developed RNA interactome profiling approach iRIL-seq, we interrogate the Hfq-associated sRNA regulatory network and establish an intracellular RNA-RNA interactome in HvKP. Our data reveal numerous interactions between sRNAs and HMV-related mRNAs, and identify a plethora of sRNAs that repress or promote HMV. One of the strongest HMV repressors is ArcZ, which is activated by the catabolite regulator CRP and targets many HMV-related genes including mlaA and fbp. We discover that MlaA and its function in phospholipid transport is crucial for capsule retention and HMV, inactivation of which abolishes Klebsiella virulence in mice. ArcZ overexpression drastically reduces bacterial burden in mice and reduces HMV in multiple hypervirulent and carbapenem-resistant clinical isolates, indicating ArcZ is a potent RNA inhibitor of bacterial pneumonia with therapeutic potential. Our work unravels a novel CRP-ArcZ-MlaA regulatory circuit of HMV and provides mechanistic insights into the posttranscriptional virulence control in a superbug of global concern.

Diverse polysaccharide production and biofilm formation abilities of clinical Klebsiella pneumoniae

Klebsiella pneumoniae infections have become a growing threat for human health. The lack of understanding of the relationship between antibiotic resistance, mucoviscosity, and biofilm formation in clinical isolates impedes our abilities to effectively predict K. pneumoniae infection outcomes. These traits are also associated with fitness in natural populations and more specifically within a host. The Multidrug-Resistant Organism Repository and Surveillance Network offers a unique opportunity into the genetic and phenotypic variabilities in the K. pneumoniae isolates encountered in the clinics today. To this end, we compared the genetic profiles of these isolates with the phenotypic biofilm formation abilities, percent mucoviscosity, and growth rates. We found most isolates formed limited biofilm, although a select group of isolates could form extremely robust biofilms. Variation in biofilm formation could not be explained by difference in growth rate, suggesting specific genetic and physical determinants. Interestingly, the most mucoid strains in the populations were lacking the genetic element regulating the mucoid phenotype and three of these isolates were able to form robust biofilms. There was a significant phenotype-genotype correlation with decreased biofilm formation and an insertion sequence in the transcriptional activator of the type III fimbrial system. Finally, confocal microscopy highlighted the structural and spatial heterogeneity of biofilm among the most robust biofilm formers not detected by traditional methods. The combination of phenotypic, genomic and image analyses allowed us to reveal an unexpected phenotypic diversity and an intricate relation between growth, mucoviscosity and specific virulence-associated genetic determinants.

Microaerobic-mediated suppression of Klebsiella pneumoniae mucoviscosity is restored by rmpD overexpression

AIMS

Hypervirulent Klebsiella pneumoniae (hvKp) causes invasive community-acquired infections in healthy individuals, and hypermucoviscosity (HMV) is the main phenotype associated with hvKp. This study investigates the impact of microaerobic environment availability on the mucoviscosity of K. pneumoniae.

METHODS AND RESULTS

By culturing 25 clinical strains under microaerobic and aerobic environments, we observed a notable reduction in mucoviscosity in microaerobic environments. RNA sequencing and qRT-PCR revealed downregulated expressions of capsule synthesis genes (galf, orf2, wzi, wza, wzb, wzc, wcaj, manC, manB, and ugd) and regulatory genes (rmpA, rmpD, and rmpC) under microaerobic conditions. Transmission electron microscopy and Indian ink staining analysis were performed, revealing that the capsular thickness of K. pneumoniae decreased by half in microaerobic conditions compared to aerobic conditions. Deletion of rmpD and rmpC caused the loss of the HMV phenotype in both aerobic and microaerobic conditions. However, compared to wild-type strain in microaerobic condition, only rmpD overexpression strain, and not rmpC overexpression strain, displayed a significant increase in capsule thickness in microaerobic conditions.

CONCLUSIONS

Microaerobic conditions can suppress the mucoviscosity of K. pneumoniae, but this suppression can be overcome by altering the expression of rmpD, indicating a specific function for rmpD in the oxygen environmental adaptation of K. pneumoniae.

Insights into the recognition of hypermucoviscous Klebsiella pneumoniae clinical isolates by innate immune lectins of the Siglec and galectin families

Klebsiella pneumoniae is an opportunistic bacterium that frequently colonizes the nasopharynx and gastrointestinal tract and can also cause severe infections when invading other tissues, particularly in immunocompromised individuals. Moreover, K. pneumoniae variants exhibiting a hypermucoviscous (HMV) phenotype are usually associated with hypervirulent strains that can produce invasive infections even in immunocompetent individuals. Major carbohydrate structures displayed on the K. pneumoniae surface are the polysaccharide capsule and the lipopolysaccharide, which presents an O-polysaccharide chain in its outermost part. Various capsular and O-chain structures have been described. Of note, production of a thick capsule is frequently observed in HMV variants. Here we examined the surface sugar epitopes of a collection of HMV and non-HMV K. pneumoniae clinical isolates and their recognition by several Siglecs and galectins, two lectin families of the innate immune system, using bacteria microarrays as main tool. No significant differences among isolates in sialic acid content or recognition by Siglecs were observed. In contrast, analysis of the binding of model lectins with diverse carbohydrate-binding specificities revealed striking differences in the recognition by galactose- and mannose-specific lectins, which correlated with the binding or lack of binding of galectins and pointed to the O-chain as the plausible ligand. Fluorescence microscopy and microarray analyses of galectin-9 binding to entire cells and outer membranes of two representative HMV isolates supported the bacteria microarray results. In addition, Western blot analysis of the binding of galectin-9 to outer membranes unveiled protein bands recognized by this galectin, and fingerprint analysis of these bands identified several proteins containing potential O-glycosylation sites, thus broadening the spectrum of possible galectin ligands on the K. pneumoniae surface. Moreover, Siglecs and galectins apparently target different structures on K. pneumoniae surfaces, thereby behaving as non-redundant complementary tools of the innate immune system.

Co-occurrence of ST412 Klebsiella pneumoniae isolates with hypermucoviscous and non-mucoviscous phenotypes in a short-term hospitalized patient

Hypermucoviscosity (HMV) is a phenotype that is commonly associated with hypervirulence in Klebsiella pneumoniae. The factors that contribute to the emergence of HMV subpopulations remain unclear. In this study, eight K. pneumoniae strains were recovered from an inpatient who had been hospitalized for 20 days. Three of the isolates exhibited a non-HMV phenotype, which was concomitant with higher biofilm formation than the other five HMV isolates. All eight isolates were highly susceptible to serum killing, albeit HMV strains were remarkably more infective than non-HMV counterparts in a mouse model of infection. Whole genome sequencing (WGS) showed that the eight isolates belonged to the K57-ST412 lineage. Average nucleotide identity (FastANIb) analysis indicated that eight isolates share 99.96% to 99.99% similarity and were confirmed to be the same clone. Through comparative genomics analysis, 12 non-synonymous mutations were found among these isolates, eight of which in the non-HMV variants, including rmpA (c.285delG) and wbaP (c.1305T > A), which are assumed to be associated with the non-HMV phenotype. Mutations in manB (c.1318G > A), dmsB (c.577C > T) and tkt (c.1928C > A) occurred in HMV isolates only. RNA-Seq revealed transcripts of genes involved in energy metabolism, carbohydrate metabolism and membrane transport, including cysP, cydA, narK, tktA, pduQ, aceB, metN, and lsrA, to be significantly dysregulated in the non-HMV strains, suggesting a contribution to HMV phenotype development. This study suggests that co-occurrence of HMV and non-HMV phenotypes in the same clonal population may be mediated by mutational mechanisms as well as by certain genes involved in membrane transport and central metabolism.

IMPORTANCE

K. pneumoniae with a hypermucoviscosity (HMV) phenotype is a community-acquired pathogen that is associated with increased invasiveness and pathogenicity, and underlying diseases are the most common comorbid risk factors inducing metastatic complications. HMV was earlier attributed to the overproduction of capsular polysaccharide, and more data point to the possibility of several causes contributing to this bacterial phenotype. Here, we describe a unique event in which the same clonal population showed both HMV and non-HMV characteristics. Studies have demonstrated that this process is influenced by mutational processes and genes related to transport and central metabolism. These findings provide fresh insight into the mechanisms behind co-occurrence of HMV and non-HMV phenotypes in monoclonal populations as well as potentially being critical in developing strategies to control the further spread of HMV K. pneumoniae.

Adaptive attenuation of virulence in hypervirulent carbapenem-resistant Klebsiella pneumoniae

The emergence of nosocomial infections caused by hypervirulent and carbapenem-resistant K. pneumoniae (hv-CRKP) has become a significant public health challenge. The genetic traits of virulence and resistance plasmids in hv-CRKP have been extensively studied; however, research on the adaptive evolution strategies of clinical strains inside the host was scarce. This study aimed to understand the effects of antibiotic treatment on the phenotype and genotype characteristics of hv-CRKP. We investigated the evolution of hv-CRKP strains isolated from the same patient to elucidate the transition between hospital invasion and colonization. A comparative genomics analysis was performed to identify single nucleotide polymorphisms in the rmpA promoter. Subsequent validation through RNA-seq and gene deletion confirmed that distinct rmpA promoter sequences exert control over the mucoid phenotype. Additionally, biofilm experiments, cell adhesion assays, and animal infection models were conducted to illuminate the influence of rmpA promoter diversity on virulence changes. We demonstrated that the P12T and P11T promoters of rmpA possess strong activity, which leads to the evolution of CRKP into infectious and virulent strains. Meanwhile, the specific sequence of polyT motifs in the rmpA promoter led to a decrease in the lethality of hv-CRKP and enhanced cell adhesion and colonization. To summarize, the rmpA promoter of hv-CRKP is utilized to control capsule production, thereby modifying pathogenicity to better suit the host's ecological environment.IMPORTANCEThe prevalence of hospital-acquired illness caused by hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) is significant, leading to prolonged antibiotic treatment. However, there are few reports on the phenotypic changes of hv-CRKP in patients undergoing antibiotic treatment. We performed a comprehensive examination of the genetic evolutionary traits of hv-CRKP obtained from the same patient and observed variations in the promoter sequences of the virulence factor rmpA. The strong activity of the promoter sequences P11T and P12T enhances the consistent production of capsule polysaccharides, resulting in an invasive strain. Conversely, weak promoter activity of P9T and P10T is advantageous for exposing pili, hence improving bacterial cell attachment ability and facilitating bacterial colonization. This finding also explains the confusion of some clinical strains carrying wild-type rmpA but exhibiting a low mucoid phenotype. This adaptive alteration facilitates the dissemination of K. pneumoniae within the hospital setting.

Relevance of the Adjuvant Effect between Cellular Homeostasis and Resistance to Antibiotics in Gram-Negative Bacteria with Pathogenic Capacity: A Study of Klebsiella pneumoniae

Antibiotic resistance has become a global issue. The most significant risk is the acquisition of these mechanisms by pathogenic bacteria, which can have a severe clinical impact and pose a public health risk. This problem assumes that bacterial fitness is a constant phenomenon and should be approached from an evolutionary perspective to develop the most appropriate and effective strategies to contain the emergence of strains with pathogenic potential. Resistance mechanisms can be understood as adaptive processes to stressful conditions. This review examines the relevance of homeostatic regulatory mechanisms in antimicrobial resistance mechanisms. We focus on the interactions in the cellular physiology of pathogenic bacteria, particularly Gram-negative bacteria, and specifically Klebsiella pneumoniae. From a clinical research perspective, understanding these interactions is crucial for comprehensively understanding the phenomenon of resistance and developing more effective drugs and treatments to limit or attenuate bacterial sepsis, since the most conserved adjuvant phenomena in bacterial physiology has turned out to be more optimized and, therefore, more susceptible to alterations due to pharmacological action.

Pyogenic liver abscess caused by an atypical hypervirulent Klebsiella pneumoniae K1-ST23 in Mexico

Hypervirulent K. pneumoniae infection has been raising worldwide and is one of the major causes of community-acquired pyogenic liver abscess. We described a case report of pyogenic liver abscess caused by an atypical hypervirulent (non-hypermucoviscous) K. pneumoniae K1 ST23 in a diabetic Asian patient who resided in Mexico. The susceptibility to antimicrobials, pathogenicity, molecular and genomic analysis were determined. A man from Guangdong (China) with a recent diagnosis of diabetes mellitus was admitted to the hospital, and he denied traveling in the last 3 months. A computed tomography revealed a right lobe liver abscess. On the third day after admission a Klebsiella pneumoniae isolate (14652) was obtained. The isolate corresponded to a susceptible K. pneumoniae with capsular type K1 and ST23 (CG23) and exhibited a non-hypermucoviscous phenotype. The isolate 14652 was genetically related to the globally distributed lineage ST23-KL1. This study describes the first case in Mexico of K. pneumoniae capsular type K1 and ST23 with an atypical hypervirulent phenotype.

Therapeutic efficacy of a K5-specific phage and depolymerase against Klebsiella pneumoniae in a mouse model of infection

Klebsiella pneumoniae has become one of the most intractable gram-negative pathogens infecting humans and animals due to its severe antibiotic resistance. Bacteriophages and protein products derived from them are receiving increasing amounts of attention as potential alternatives to antibiotics. In this study, we isolated and investigated the characteristics of a new lytic phage, P1011, which lyses K5 K. pneumoniae specifically among 26 serotypes. The K5-specific capsular polysaccharide-degrading depolymerase dep1011 was identified and expressed. By establishing murine infection models using bovine strain B16 (capable of supporting phage proliferation) and human strain KP181 (incapable of sustaining phage expansion), we explored the safety and efficacy of phage and dep1011 treatments against K5 K. pneumoniae. Phage P1011 resulted in a 60% survival rate of the mice challenged with K. pneumoniae supporting phage multiplication, concurrently lowering the bacterial burden in their blood, liver, and lungs. Unexpectedly, even when confronted with bacteria impervious to phage multiplication, phage therapy markedly decreased the number of viable organisms. The protective efficacy of the depolymerase was significantly better than that of the phage. The depolymerase achieved 100% survival in both treatment groups regardless of phage propagation compatibility. These findings indicated that P1011 and dep1011 might be used as potential antibacterial agents to control K5 K. pneumoniae infection.

Antibody responses in Klebsiella pneumoniae bloodstream infection: a cohort study

Background

Klebsiella pneumonia (Kpn) is the fourth leading cause of infection-related deaths globally, yet little is known about human antibody responses to invasive Kpn. In this study, we sought to determine whether the O-specific polysaccharide (OPS) antigen, a vaccine candidate, is immunogenic in humans with Kpn bloodstream infection (BSI). We also sought to define the cross-reactivity of human antibody responses among structurally related Kpn OPS subtypes and to assess the impact of capsule production on OPS-targeted antibody binding and function.

Methods

We measured plasma antibody responses to OPS (and MrkA, a fimbrial protein) in a cohort of patients with Kpn BSI and compared these with controls, including a cohort of healthy individuals and a cohort of individuals with Enterococcus BSI. We performed flow cytometry to measure the impact of Kpn capsule production on whole cell antibody binding and complement deposition, utilizing patient isolates with variable levels of capsule production and isogenic capsule-deficient strains derived from these isolates.

Findings

We enrolled 69 patients with Kpn BSI. Common OPS serotypes accounted for 57/69 (83%) of infections. OPS was highly immunogenic in patients with Kpn BSI, and peak OPS-IgG antibody responses in patients were 10 to 30-fold higher than antibody levels detected in healthy controls, depending on the serotype. There was significant cross-reactivity among structurally similar OPS subtypes, including the O1v1/O1v2, O2v1/O2v2 and O3/O3b subtypes. Physiological amounts of capsule produced by both hyperencapsulated and non-hyperencapsulated Kpn significantly inhibited OPS-targeted antibody binding and function.

Interpretation

OPS was highly immunogenic in patients with Kpn BSI, supporting its potential as a candidate vaccine antigen. The strong cross-reactivity observed between similar OPS subtypes in humans with Kpn BSI suggests that it may not be necessary to include all subtypes in an OPS-based vaccine. However, these observations are tempered by the fact that capsule production, even in non-highly encapsulated strains, has the potential to interfere with OPS antibody binding. This may limit the effectiveness of vaccines that exclusively target OPS.

Funding

National Institute of Allergy and Infectious Diseases at the National Institutes of Health.

Research in Context

Evidence before this study: Despite the potential of O-specific polysaccharide (OPS) as a vaccine antigen against Klebsiella pneumoniae (Kpn), the immunogenicity of OPS in humans remains largely unstudied, creating a significant knowledge gap with regard to vaccine development. A search of PubMed for publications up to March 18, 2024, using the terms " Klebsiella pneumoniae " and "O-specific polysaccharide" or "O-antigen" or "lipopolysaccharide" revealed no prior studies addressing OPS antibody responses in humans with Kpn bloodstream infections (BSI). One prior study 1 evaluated antibody response to a single lipopolysaccharide (which contains one subtype of OPS) in humans with invasive Kpn infection; however, in this study OPS typing of the infecting strains and target antigen were not described. Added value of this study: Our investigation into OPS immunogenicity in a human cohort marks a significant advance. Analyzing plasma antibody responses in 69 patients with Kpn BSI, we found OPS to be broadly immunogenic across all the types and subtypes examined, and there was significant cross-reactivity among structurally related OPS antigens. We also demonstrated that Kpn capsule production inhibit OPS antibody binding and the activation of complement on the bacterial surface, even in classical Kpn strains expressing lower levels of capsule.Implications of all the available evidence: While the immunogenicity and broad cross-reactivity of OPS in humans with Kpn BSI suggests it is a promising vaccine candidate, the obstruction of OPS antibody binding and engagement by physiologic levels of Kpn capsule underscores the potential limitations of an exclusively OPS-antigen based vaccine for Kpn. Our study provides insights for the strategic development of vaccines aimed at combating Kpn infections, an important antimicrobial resistant pathogen.

Predicting Antibiotic Tolerance in hvKP and cKP Respiratory Infections Through Biofilm Formation Analysis and Its Resistance Implications

Introduction

Respiratory infections are a major global health concern, with Klebsiella pneumoniae standing out due to its evolving antibiotic resistance. This study compares the resistance profiles of hypervirulent Klebsiella pneumoniae (hvKP) and classical Klebsiella pneumoniae (cKP), aiming to shed light on their clinical implications.

Methods

We analyzed 86 cases, comprising 42 hvKP and 44 cKP strains, using comprehensive antimicrobial susceptibility testing and clinical data evaluation to assess antibiotic tolerance and resistance mechanisms.

Results

Our findings reveal distinct resistance patterns between hvKP and cKP, highlighting the role of chromosomal mutations and plasmid-mediated gene transfer in conferring antibiotic resistance. Notably, hvKP strains exhibited unique resistance trends, including the production of extended-spectrum β-lactamases (ESBLs) and carbapenemases, differing from those of cKP.

Discussion

This research underscores the importance of continuous surveillance and the development of targeted therapies against antibiotic-resistant Klebsiella pneumoniae. It emphasizes the critical need for judicious antibiotic use and novel therapeutic approaches to combat respiratory infections caused by these increasingly resistant pathogens.

Comprehensive study reveals phenotypic heterogeneity in Klebsiella pneumoniae species complex isolates

Here, we conducted a comprehensive analysis of 356 Klebsiella pneumoniae species complex (KpSC) isolates that were classified as classical (cl), presumptive hypervirulent (p-hv) and hypermucoviscous-like (hmv-like). Overall, K. pneumoniae (82.3%), K. variicola (2.5%) and K. quasipneumoniae (2.5%) were identified. These isolates comprised 321 cl-KpSC, 7 p-hv-KpSC and 18 hmv-like-KpSC. A large proportion of cl-KpSC isolates were extended-spectrum-β-lactamases (ESBLs)-producers (64.4%) and 3.4% of isolates were colistin-resistant carrying carbapenemase and ESBL genes. All p-hv-KpSC showed an antibiotic susceptible phenotype and hmv-like isolates were found to be ESBL-producers (8/18). Assays for capsule production and capsule-dependent virulence phenotypes and whole-genome sequencing (WGS) were performed in a subset of isolates. Capsule amount differed in all p-hv strains and hmv-like produced higher capsule amounts than cl strains; these variations had important implications in phagocytosis and virulence. Murine sepsis model showed that most cl strains were nonlethal and the hmv-like caused 100% mortality with 3 × 108 CFUs. Unexpectedly, 3/7 (42.9%) of p-hv strains required 108 CFUs to cause 100% mortality (atypical hypervirulent), and 4/7 (57.1%) strains were considered truly hypervirulent (hv). Genomic analyses confirmed the diverse population, including isolates belonging to hv clonal groups (CG) CG23, CG86, CG380 and CG25 (this corresponded to the ST3999 a novel hv clone) and MDR clones such as CG258 and CG147 (ST392) among others. We noted that the hmv-like and hv-ST3999 isolates showed a close phylogenetic relationship with cl-MDR K. pneumoniae. The information collected here is important to understand the evolution of clinically important phenotypes such as hypervirulent and ESBL-producing-hypermucoviscous-like amongst the KpSC in Mexican healthcare settings. Likewise, this study shows that mgrB inactivation is the main mechanism of colistin resistance in K. pneumoniae isolates from Mexico.

Capsules and their traits shape phage susceptibility and plasmid conjugation efficiency

Bacterial evolution is affected by mobile genetic elements like phages and conjugative plasmids, offering new adaptive traits while incurring fitness costs. Their infection is affected by the bacterial capsule. Yet, its importance has been difficult to quantify because of the high diversity of confounding mechanisms in bacterial genomes such as anti-viral systems and surface receptor modifications. Swapping capsule loci between Klebsiella pneumoniae strains allowed us to quantify their impact on plasmid and phage infection independently of genetic background. Capsule swaps systematically invert phage susceptibility, revealing serotypes as key determinants of phage infection. Capsule types also influence conjugation efficiency in both donor and recipient cells, a mechanism shaped by capsule volume and conjugative pilus structure. Comparative genomics confirmed that more permissive serotypes in the lab correspond to the strains acquiring more conjugative plasmids in nature. The least capsule-sensitive pili (F-like) are the most frequent in the species' plasmids, and are the only ones associated with both antibiotic resistance and virulence factors, driving the convergence between virulence and antibiotics resistance in the population. These results show how traits of cellular envelopes define slow and fast lanes of infection by mobile genetic elements, with implications for population dynamics and horizontal gene transfer.

Comparative analysis of multidrug-resistant Klebsiella pneumoniae strains of food and human origin reveals overlapping populations

Given the increasing incidence of multidrug-resistant (MDR) Klebsiella pneumoniae infections, it is of great interest to investigate the risk of transmission associated with the prevalence of this pathogen. Some studies have described fresh raw poultry meat as a reservoir of MDR K. pneumoniae, including clinically relevant sequence types (ST) and extended-spectrum β-lactamase (ESBL) strains, indicating possible consumer exposure. This study compared 47 MDR strains of K. pneumoniae from poultry meat and human clinical isolates to assess similarities, including analysis of antimicrobial resistance profiles and virulence factors involved in infection. In addition, several biofilm culture methods were evaluated for reproducible assessment of biofilm formation in K. pneumoniae strains. Globally, no association between strain origin and STs, hypermucoviscosity, biofilm formation or serum resistance could be found between isolates of food and clinical origin, nor an associated AMR pattern, suggesting overlapping populations. We found that LB supplemented with glucose in microaerobiosis was the best discrimination condition for biofilm formation in the active attachment biofilm cultivation model. The biofilm formation capacity was strongly dependent on culture conditions, with a strain-specific response, but only a minor increase in biofilm levels was recorded in clinical K. pneumoniae populations. Our results suggest that a similar risk of zoonosis transmission from potentially virulent foodborne strains previously observed in E. coli is also present in this high-priority pathogen. This study further confirms that foodborne isolates of K. pneumoniae pose a risk to consumers and therefore this pathogen should be included in the surveillance of foodborne pathogens with high risk of MDR infections and therapeutic failure.

Differentiation of hypervirulent and classical Klebsiella pneumoniae with acquired drug resistance

Distinguishing hypervirulent (hvKp) from classical Klebsiella pneumoniae (cKp) strains is important for clinical care, surveillance, and research. Some combinations of iucA, iroB, peg-344, rmpA, and rmpA2 are most commonly used, but it is unclear what combination of genotypic or phenotypic markers (e.g., siderophore concentration, mucoviscosity) most accurately predicts the hypervirulent phenotype. Furthermore, acquisition of antimicrobial resistance may affect virulence and confound identification. Therefore, 49 K. pneumoniae strains that possessed some combinations of iucA, iroB, peg-344, rmpA, and rmpA2 and had acquired resistance were assembled and categorized as hypervirulent hvKp (hvKp) (N = 16) or cKp (N = 33) via a murine infection model. Biomarker number, siderophore production, mucoviscosity, virulence plasmid's Mash/Jaccard distances to the canonical pLVPK, and Kleborate virulence score were measured and evaluated to accurately differentiate these pathotypes. Both stepwise logistic regression and a CART model were used to determine which variable was most predictive of the strain cohorts. The biomarker count alone was the strongest predictor for both analyses. For logistic regression, the area under the curve for biomarker count was 0.962 (P = 0.004). The CART model generated the classification rule that a biomarker count = 5 would classify the strain as hvKP, resulting in a sensitivity for predicting hvKP of 94% (15/16), a specificity of 94% (31/33), and an overall accuracy of 94% (46/49). Although a count of ≥4 was 100% (16/16) sensitive for predicting hvKP, the specificity and accuracy decreased to 76% (25/33) and 84% (41/49), respectively. These findings can be used to inform the identification of hvKp.IMPORTANCEHypervirulent Klebsiella pneumoniae (hvKp) is a concerning pathogen that can cause life-threatening infections in otherwise healthy individuals. Importantly, although strains of hvKp have been acquiring antimicrobial resistance, the effect on virulence is unclear. Therefore, it is of critical importance to determine whether a given antimicrobial resistant K. pneumoniae isolate is hypervirulent. This report determined which combination of genotypic and phenotypic markers could most accurately identify hvKp strains with acquired resistance. Both logistic regression and a machine-learning prediction model demonstrated that biomarker count alone was the strongest predictor. The presence of all five of the biomarkers iucA, iroB, peg-344, rmpA, and rmpA2 was most accurate (94%); the presence of ≥4 of these biomarkers was most sensitive (100%). Accurately identifying hvKp is vital for surveillance and research, and the availability of biomarker data could alert the clinician that hvKp is a consideration, which, in turn, would assist in optimizing patient care.

Distinct epigenetic signatures of classical and hypervirulent Klebsiella pneumoniae

Emergence and spread of the hypervirulent pathotype of Klebsiella pneumoniae have significantly increased infection rates in community as well as healthcare settings. There is an increasing interest to identify discriminating features between classical K. pneumoniae (cKp) and hypervirulent K. pneumoniae (hvKp) to facilitate our understanding of the rapid emergence and dissemination of the hypervirulent pathotype. Here, we sought to identify unique epigenetic signatures of hvKp pathotype that differ from its classical counterpart using single-base resolution methylome analysis of native DNA sequencing on the Oxford Nanopore Technologies platform. The overall global adenine methylation in GATC motifs (i.e., Dam methylation motif) and cytosine methylation in CCWGG motifs (i.e., Dcm methylation motif) were significantly higher in hvKp isolates compared to that in cKp isolates, irrespective of their position in chromosomes or putative extra-chromosomal genetic elements. Notably, we observed significant enrichment of hypermethylated GATC and CCWGG motifs in the virulome of hvKp compared to hvKp genes not directly associated with virulence. We also observed increased methylation of GATC and CCWGG motifs in the capsule synthesis locus of hvKp isolates compared to cKp isolates. Furthermore, we identified several differentially methylated genes (DMGs) between the two pathotypes; interestingly, these DMGs include metal ion transporters, multidrug efflux pumps, transcriptional regulators of stress response, and genes associated with biofilm formation. Our results highlight hypermethylation of GATC and CCWGG motifs as unique epigenetic signatures of hvKp isolates.IMPORTANCEHypervirulent Klebsiella pneumoniae (hvKp) is a more virulent and rapidly evolving hypermucoviscous pathotype of classical K. pneumoniae (cKp). The hypervirulent pathotype is a major public health concern and is associated with high infection rates in community as well as hospital settings. With the recent emergence of multidrug-resistant hvKp, it has become imperative to investigate non-classical mechanisms such as epigenetics in addition to canonical biochemical and genetic mechanisms that delineate and differentiate the hypervirulent pathotype from its classical counterpart. Here, we identify genome-wide differences in adenine and cytosine methylation marks at well-characterized motifs between the two pathotypes. Overall, significantly higher levels of methylation were observed across chromosomal DNA and extrachromosomal elements in hvKp compared to cKp. Among hvKp isolates, the genes associated with virulence are particularly enriched for methylation marks. Our findings shed light on how epigenetic signatures may help distinguish the pathogenic potential of bacteria.

Chasing the landscape for intrahospital transmission and evolution of hypervirulent carbapenem-resistant Klebsiella pneumoniae

The spread of hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKP) is a global health concern. Here, we report the intrahospital colonization and spread of Hv-CRKP isolates in a tertiary hospital from 2017 to 2022. Analyses of 90 nonredundant CRKP isolates from 72 patients indicated that Hv-CRKP transferability relies on the dominant ST11-K64 clone. Whole-genome sequencing of 11 representative isolates gave 31 complete plasmid sequences, including 12 KPC-2 resistance carriers and 10 RmpA virulence vehicles. Apart from the binary vehicles, we detected two types of fusion plasmids, favoring the cotransfer of RmpA virulence and KPC-2 resistance. The detection of ancestry/relic plasmids enabled us to establish genetic mechanisms by which rare fusion plasmids form. Unexpectedly, we found a total of five rmpA promoter variants (P9T-P13T) exhibiting distinct activities and varying markedly in their geographic distributions. CRISPR/Cas9 manipulation confirmed that an active PT11-rmpA regulator is a biomarker for the "high-risk" ST11-K64/CRKP clone. These findings suggest clonal spread and clinical evolution of the prevalent ST11-K64/Hv-CRKP clones. Apart from improved public awareness of Hv-CRKP convergence, our findings might benefit the development of surveillance (and/or intervention) strategies for the dominant ST11-K64 lineage of the Hv-CRKP population in healthcare sectors.

A heptavalent O-antigen bioconjugate vaccine exhibits differential functional antibody responses against diverse Klebsiella pneumoniae isolates

Klebsiella pneumoniae is a concerning pathogen that is now the leading cause of neonatal sepsis and is increasingly difficult to treat due to heightened antibiotic resistance. Thus, there is an urgent need for preventive and effective immunotherapies targeting K. pneumoniae. Vaccination represents a tractable approach to combat this resistant bacterium in some settings; however, there is currently not a licensed K. pneumoniae vaccine available. K. pneumoniae surface polysaccharides, including the terminal O-antigen polysaccharides of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting seven of the predominant O-antigen subtypes in K. pneumoniae. Each of the seven bioconjugates were immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains, including suspected hypervirulent strains, all expressing different O-antigen and capsular polysaccharide combinations. Further, sera from vaccinated mice induced complement-mediated killing of many of these K. pneumoniae strains. Finally, we found that increased quantity of capsule interferes with O-antigen antibodies' ability to bind and mediate killing of some K. pneumoniae strains, including those carrying hypervirulence-associated genes. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits promising efficacy against some, but not all, K. pneumoniae isolates.

Antibacterial and antibiofilm activity of 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H pyrazoles and thiazoles in multidrug-resistant pathogens

To find novel antibiotic drugs, six 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-1H derivatives named 1b, 1d (pyrazoles), 2a, 2b, 2c, and 2d (thiazoles) were evaluated in silico and in vitro. The in silico analyses were based on ADME pharmacokinetic parameters (absorption, distribution, metabolism, and excretion). The in vitro antibacterial activity was evaluated in Gram-positive and Gram-negative species (Staphylococcus aureus ATCC® 25904, Staphylococcus epidermidis ATCC® 35984, Klebsiella pneumoniae ATCC® 700603, and Acinetobacter baumannii ATCC® 19606), by determination of minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), kinetics curve, and antibiofilm assays. As results, the azoles have activity against the Gram-negative species K. pneumoniae ATCC® 700603 and A. baumannii ATCC® 19606. No antibacterial activity was observed for the Gram-positive bacteria evaluated. Thus, the azoles were evaluated against clinical isolates of K. pneumoniae carbapenemase (KPC) and A. baumannii multidrug-resistant (Ab-MDR). All azoles have antibacterial activity against Ab-MDR isolates (Gram-negative) with MIC values between 512 μg/mL and 1,024 μg/mL. Against KPC isolates the azoles 1b, 1d, and 2d present antibacterial activity (MIC = 1,024 μg/mL). In the kinetics curve assay, the 1b and 1d pyrazoles reduced significantly viable cells of Ab-MDR isolates and additionally inhibited 86.6 to 95.8% of the biofilm formation. The in silico results indicate high possibility to permeate the blood-brain barrier (2b) and was predict human gastrointestinal absorption (all evaluated azoles). Considering that the research and development of new antibiotics is a priority for drug-resistant pathogens, our study revealed the antibacterial and antibiofilm activity of novel azoles against K. pneumoniae and A. baumannii pathogens.

Genome sequence of a virulent and hypermucoviscous-like Klebsiella michiganensis clinical isolate

OBJECTIVES

The hypermucoviscous-like phenotype has been described in Klebsiella pneumoniae species complex (KpSC) and was described as a contributor of increased virulence. This study described the characterization and whole-genome sequencing of an antibiotic susceptible and hypermucoviscous-like Klebsiella michiganensis 9273 clinical isolate.

DATA DESCRIPTION

Here, we report the genome sequence of a K. michiganensis clinical isolate obtained from a urinary tract infection exhibiting the hypermucoviscous-like phenotype. The draft genome sequence consisted of 145 contigs and ~ 6.6 Mb genome size. The annotation revealed 6648 coding DNA sequences and 56 tRNA genes. The strain belongs to the sequence type (ST) 50, and the OXY-1 beta-lactam resistance gene, aph(3')-Ia gene for aminoglycoside resistance and multidrug efflux pumps were identified. The fyuA siderophore receptor of yersiniabactin siderophore was identified. Increased virulence was observed in Galleria mellonella larvae model and increased capsule production was determined by uronic acid quantification. The clinical implications of this phenotype are unknown, but the patient outcome might worsen compared to susceptible- or MDR-classical K. michiganensis isolates.

Differentiation of hypervirulent and classical Klebsiella pneumoniae with acquired drug resistance

Distinguishing hypervirulent (hvKp) from classical Klebsiella pneumoniae (cKp) strains is important for clinical care, surveillance, and research. Some combination of iucA, iroB, peg-344, rmpA, and rmpA2 are most commonly used, but it is unclear what combination of genotypic or phenotypic markers (e.g. siderophore concentration, mucoviscosity) most accurately predicts the hypervirulent phenotype. Further, acquisition of antimicrobial resistance may affect virulence and confound identification. Therefore, 49 K. pneumoniae strains that possessed some combination of iucA, iroB, peg-344, rmpA, and rmpA2 and had acquired resistance were assembled and categorized as hypervirulent hvKp (hvKp) (N=16) or cKp (N=33) via a murine infection model. Biomarker number, siderophore production, mucoviscosity, virulence plasmid's Mash/Jaccard distances to the canonical pLVPK, and Kleborate virulence score were measured and evaluated to accurately differentiate these pathotypes. Both stepwise logistic regression and a CART model were used to determine which variable was most predictive of the strain cohorts. The biomarker count alone was the strongest predictor for both analyses. For logistic regression the area under the curve for biomarker count was 0.962 (P = 0.004). The CART model generated the classification rule that a biomarker count = 5 would classify the strain as hvKP, resulting in a sensitivity for predicting hvKP of 94% (15/16), a specificity of 94% (31/33), and an overall accuracy of 94% (46/49). Although a count of ≥ 4 was 100% (16/16) sensitive for predicting hvKP, the specificity and accuracy decreased to 76% (25/33) and 84% (41/49) respectively. These findings can be used to inform the identification of hvKp.

Importance

Hypervirulent Klebsiella pneumoniae (hvKp) is a concerning pathogen that can cause life-threatening infections in otherwise healthy individuals. Importantly, although strains of hvKp have been acquiring antimicrobial resistance, the effect on virulence is unclear. Therefore, it is of critical importance to determine whether a given antimicrobial resistant K. pneumoniae isolate is hypervirulent. This report determined which combination of genotypic and phenotypic markers could most accurately identify hvKp strains with acquired resistance. Both logistic regression and a machine-learning prediction model demonstrated that biomarker count alone was the strongest predictor. The presence of all 5 of the biomarkers iucA, iroB, peg-344, rmpA, and rmpA2 was most accurate (94%); the presence of ≥ 4 of these biomarkers was most sensitive (100%). Accurately identifying hvKp is vital for surveillance and research, and the availability of biomarker data could alert the clinician that hvKp is a consideration, which in turn would assist in optimizing patient care.

The Type VI Secretion System Contributes to the Invasiveness of Liver Abscess Caused by Klebsiella pneumoniae

BACKGROUND

Klebsiella pneumoniae liver abscess (KPLA) with extrahepatic migratory infections is defined as invasive KPLA (IKPLA). The type VI secretion system (T6SS) is involved in the pathogenesis of KPLA. We hypothesized that T6SS plays a role in IKPLA.

METHODS

16S ribosomal RNA gene sequencing was performed on abscess samples. Polymerase chain reaction (PCR) and reverse-transcription PCR (RT-PCR) was used to validate the expression difference of T6SS hallmark genes. In vitro and in vivo experiments were performed to identify the pathogenic feature of T6SS.

RESULTS

PICRUSt2 predicted that the T6SS-related genes were notably enriched in the IKPLA group. PCR detection of T6SS hallmark genes (hcp, vgrG, and icmF) showed that 197 (81.1%) were T6SS-positive strains. The T6SS-positive strain detection rate in the IKPLA group was higher than in the KPLA group (97.1% vs 78.4%; P < .05). RT-PCR showed that the hcp expression level was markedly increased in IKPLA isolates (P < .05). The T6SS-positive isolates showed higher survival against serum and neutrophil killing (all P < .05). The T6SS-positive K pneumoniae-infected mice had a shorter survival time, higher mortality, and an increased interleukin 6 expression in the liver and lungs (all P < .05).

CONCLUSIONS

T6SS is an essential virulence factor for K pneumoniae and contributes to IKPLA.

Staphylococcus aureus Adaptation to the Skin in Health and Persistent/Recurrent Infections

Staphylococcus aureus is a microorganism with an incredible capability to adapt to different niches within the human body. Approximately between 20 and 30% of the population is permanently but asymptomatically colonized with S. aureus in the nose, and another 30% may carry S. aureus intermittently. It has been established that nasal colonization is a risk factor for infection in other body sites, including mild to severe skin and soft tissue infections. The skin has distinct features that make it a hostile niche for many bacteria, therefore acting as a strong barrier against invading microorganisms. Healthy skin is desiccated; it has a low pH at the surface; the upper layer is constantly shed to remove attached bacteria; and several host antimicrobial peptides are produced. However, S. aureus is able to overcome these defenses and colonize this microenvironment. Moreover, this bacterium can very efficiently adapt to the stressors present in the skin under pathological conditions, as it occurs in patients with atopic dermatitis or suffering chronic wounds associated with diabetes. The focus of this manuscript is to revise the current knowledge concerning how S. aureus adapts to such diverse skin conditions causing persistent and recurrent infections.

Prevalence of multidrug-resistant hypervirulent Klebsiella pneumoniae without defined hypervirulent biomarkers in Anhui, China: a new dimension of hypervirulence

Klebsiella pneumoniae is an opportunistic pathogen that mainly causes nosocomial infections and hospital-associated pneumonia in elderly and immunocompromised people. However, multidrug-resistant hypervirulent K. pneumoniae (MDR-hvKp) has emerged recently as a serious threat to global health that can infect both immunocompromised and healthy individuals. It is scientifically established that plasmid-mediated regulator of mucoid phenotype genes (rmpA and rmpA2) and other virulence factors (aerobactin and salmochelin) are mainly responsible for this phenotype. In this study, we collected 23 MDR-hvKp isolates and performed molecular typing, whole genome sequencing, comparative genomic analysis, and phenotypic experiments, including the Galleria mellonella infection model, to reveal its genetic and phenotypic features. Meanwhile, we discovered two MDR-hvKp isolates (22122315 and 22091569) that showed a wide range of hypervirulence and hypermucoviscosity without rmpA and rmpA2 and any virulence factors. In phenotypic experiments, isolate 22122315 showed the highest hypervirulence (infection model) with significant mucoviscosity, and conversely, isolate 22091569 exhibited the highest mucoviscosity (string test) with higher virulence compared to control. These two isolates carried carbapenemase (blaKPC - 2), β-lactamase (blaOXA - 1, blaTEM - 1B), extended-spectrum β-lactamase (ESBL) genes (blaCTX - M - 15, blaSHV - 106), outer membrane protein-coding genes (ompA), fimbriae encoding genes (ecpABCDER), and enterobactin coding genes (entAB, fepC). In addition, single nucleotide polymorphism analysis indicated that both isolates, 22122315 and 22091569, were found to have novel mutations in loci FEBNDAKP_03184 (c. 2084A > C, p. Asn695Thr), and EOFMAFIB_02276 (c. 1930C > A, p. Pro644Thr), respectively. Finally, NCBI blast analysis suggested these mutations are located in the wzc of the capsule polysaccharide (cps) region and are responsible for putative tyrosine kinase. This study would be a strong reference for enhancing the current understanding of identifying the MDR-hvKp isolates that lacked both mucoid regulators and virulence factors.

Klebsiella pneumoniae: adaptive immune landscapes and vaccine horizons

Klebsiella pneumoniae is among the most common antibiotic-resistant pathogens causing nosocomial infections. Additionally, it is a leading cause of neonatal sepsis and childhood mortality across the globe. Despite its clinical importance, we are only beginning to understand how the mammalian adaptive immune system responds to this pathogen. Further, many studies investigating potential K. pneumoniae vaccine candidates or alternative therapies have been launched in recent years. Here, we review the current state of knowledge on the adaptive immune response to K. pneumoniae infections and progress towards developing vaccines and other therapies to combat these infections.

The role of integration host factor in biofilm and virulence of high-alcohol-producing Klebsiella pneumoniae

Klebsiella pneumoniae is a well-known human nosocomial pathogen with an arsenal of virulence factors, including capsular polysaccharides (CPS), fimbriae, flagella, and lipopolysaccharides (LPS). Our previous study found that alcohol acted as an essential virulence factor for high-alcohol-producing K. pneumoniae (HiAlc Kpn). Integration host factor (IHF) is a nucleoid-associated protein that functions as a global virulence regulator in Escherichia coli. However, the regulatory role of IHF in K. pneumoniae remains unknown. In the present study, we found that deletion of ihfA or ihfB resulted in a slight defect in bacterial growth, a severe absence of biofilm formation and cytotoxicity, and a significant reduction in alcohol production. RNA sequencing differential gene expression analysis showed that compared with the wild-type control, the expression of many virulence factor genes was downregulated in ΔihfA and ΔihfB strains, such as those related to CPS (rcsA, galF, wzi, and iscR), LPS (rfbABCD), type I and type III fimbriae (fim and mrk operon), cellulose (bcs operon), iron transporter (feoABC, fhuA, fhuF, tonB, exbB, and exbD), quorum sensing (lsr operon and sdiA), type II secretion system (T2SS) and type VI secretion system (T6SS) (tssG, hcp, and gspE). Of these virulence factors, CPS, LPS, fimbriae, and cellulose are involved in biofilm formation. In addition, IHF could affect the alcohol production by regulating genes related to glucose intake (ptsG), pyruvate formate-lyase, alcohol dehydrogenase, and the tricarboxylic acid (TCA) cycle. Our data provided new insights into the importance of IHF in regulating the virulence of HiAlc Kpn. IMPORTANCE Klebsiella pneumoniae is a well-known human nosocomial pathogen that causes various infectious diseases, including urinary tract infections, hospital-acquired pneumonia, bacteremia, and liver abscesses. Our previous studies demonstrated that HiAlc Kpn mediated the development of nonalcoholic fatty liver disease by producing excess endogenous alcohol in vivo. However, the regulators regulating the expression of genes related to metabolism, biofilm formation, and virulence of HiAlc Kpn remain unclear. In this study, the regulator IHF was found to positively regulate biofilm formation and many virulence factors including CPS, LPS, type I and type III fimbriae, cellulose, iron transporter, AI-2 quorum sensing, T2SS, and T6SS in HiAlc Kpn. Furthermore, IHF positively regulated alcohol production in HiAlc Kpn. Our results suggested that IHF could be a potential drug target for treating various infectious diseases caused by K. pneumoniae. Hence, the regulation of different virulence factors by IHF in K. pneumoniae requires further investigation.

Two-Component Response Regulator OmpR Regulates Mucoviscosity through Energy Metabolism in Klebsiella pneumoniae

Hypermucoviscosity is a hallmark of hypervirulent Klebsiella pneumoniae (hvKP). However, the molecular basis of its regulation is largely unknown. We hypothesize that hypermucoviscosity is modulated via two-component signal transduction systems (TCSs). In-frame deletion mutants of all 33 response regulators of hvKP ATCC43816 were generated using CRISPR/CAS and evaluated for their impacts on hypermucoviscosity. The response regulator OmpR is required for hypermucoviscosity in vitro and virulence in vivo in a mouse pneumonia model. The ΔompR mutant lost its mucoidy but retained its capsule level and comparable rmpADC expression, so transcriptomic analysis by RNA-Seq was performed to identify differentially expressed genes (DEGs) in ΔompR mutant. The top 20 Gene Ontology terms of 273 DEGs belong to purine ribonucleotide triphosphate biosynthetic and metabolic process, transmembrane transport, and amino acid metabolism. Among the overexpressed genes in the ΔompR mutant, the atp operon encoding F-type ATP synthase and the gcvTHP encoding glycine cleavage system were characterized further as overexpression of either operon reduced the mucoviscosity and increased the production of ATP. Furthermore, OmpR directly bound the promoter region of the atp operon, not the gcvTHP, suggesting that OmpR regulates the expression of the atp operon directly and gcvTHP indirectly. Hence, the loss of OmpR led to the overexpression of F-type ATP synthase and glycine cleavage system, which altered the energetic status of ΔompR cells and contributed to the subsequent reduction in the mucoviscosity. Our study has uncovered a previously unknown regulation of bacterial metabolism by OmpR and its influence on hypermucoviscosity. IMPORTANCE Hypermucoviscosity is a critical virulent factor for Klebsiella pneumoniae infections, and its regulation remains poorly understood at the molecular level. This study aims to address this knowledge gap by investigating the role of response regulators in mediating hypermucoviscosity in K. pneumoniae. We screened 33 response regulators and found that OmpR is essential for hypermucoviscosity and virulence of K. pneumoniae in a mouse pneumonia model. Transcriptomic analysis uncovered that genes involved in energy production and metabolism are highly upregulated in the ΔompR mutant, suggesting a potential link between bacterial energy status and hypermucoviscosity. Overexpression of those genes increased production of ATP and reduced mucoviscosity, recapitulating the ΔompR mutant phenotype. Our findings provide new insights into the regulation of K. pneumoniae hypermucoviscosity by a two-component signal transduction system, highlighting the previously unknown role of OmpR in regulating bacterial energy status and its influence on hypermucoviscosity.

Hypermucoviscous Klebsiella pneumoniae: A Hypervirulent Strain Masquerading as Metastasis

Hypermucoviscous Klebsiella pneumoniae (HvKP) is a hypervirulent strain of Klebsiella that causes metastatic spread and life-threatening infection. While it is more common among people of Asian descent, it has been increasingly reported globally among people of other ethnicities as well. We report a case of pan-susceptible HvKP infection in a male patient of Asian descent who has been living in the US for 20 years. It caused a liver abscess, perigastric abscess, perisplenic abscess, multifocal pneumonia, septic emboli, and tricuspid valve infective endocarditis. He was treated with ceftriaxone, but his septic shock was refractory, ultimately leading to death. This case highlights the severity of infection caused by this strain, and its ability to present with radiographic signs suggestive of malignancy with metastasis. This case also suggests that this strain can become pathogenic after a very prolonged period of gastrointestinal colonization.

Clinical Spectrum and Outcomes of Cryptogenic Klebsiella pneumoniae Liver Abscess in the Americas: A Scoping Review

(1) Background: Cryptogenic Klebsiella pneumoniae liver abscesses are an invasive infection with or without extra hepatic involvement in the absence of hepatobiliary disease or abdominal malignancy. Most of the evidence has emanated from reports from Asia, and previous studies in the Americas have limited clinical characterization. (2) Methods: To understand this syndrome's characteristics on our continent, we conducted a scoping review to identify adult cases of idiopathic, community-acquired monomicrobial K. pneumoniae liver abscess in the Americas. (3) Results: We identified 144 cases spanning 1978-2022. Most cases were reported in males that had traveled or migrated from Southeast or East Asia with diabetes mellitus. Extrahepatic involvement and bacteremia were common, including seeding to the lungs, ocular structures, and central nervous system. Although limited by sample size, the most commonly reported genes were magA or rmpA. Concomitant percutaneous drainage and third generation cephalosporins (alone or in combination with other antibiotics) were frequently used, yet pooled fatality occurred in 9% of the reported cases. (4) Conclusions: The features of cryptogenic K. pneumoniae liver abscess in the Americas mirror those described in Asia, confirming its global dissemination. This condition is increasingly being reported in our continent and carries significant clinical impact due to its systemic invasiveness.

Different regulatory mechanisms of the capsule in hypervirulent Klebsiella pneumonia: "direct" wcaJ variation vs. "indirect" rmpA regulation

Introduction

Hypervirulent Klebsiella pneumoniae produce an increased amount of capsular substance and are associated with a hypermucoviscous phenotype. Capsule production is regulated by capsular regulatory genes and capsular gene cluster variations. In the present study, we focus on the effect of rmpA and wcaJon capsule biosynthesis.

Methods

Phylogenetic trees were constructed to analyze wcaJ and rmpA sequence diversity in different serotypes hypervirulent strains. Then mutant strains (K2044ΔwcaJ, K2044K1wcaJ, K2044K2wcaJand K2044K64wcaJ) were used to verify the effects of wcaJ and its diversity on capsule synthesis and strain virulence. Furthmore, the role of rmpA in capsular synthesis and its mechanisms were detected in K2044ΔrmpA strain.

Results

RmpA sequences are conversed in different serotypes. And rmpA promoted the production of hypercapsules by simultaneously acting on three promoters in cps cluster. Whereas wcaJ, its sequences are different in different serotypes, and its loss result in the termination of capsular synthesis. Moreover, the results verified that K2 wcaJ could form hypercapsule in K2044 strains (K1 serotype), but K64 wcaJ could not.

Discussion

The interaction of multiple factors is involved in capsule synthesis, including wcaJ and rmpA. RmpA, an known conserved capsular regulator gene, acts on cps cluster promoters to promote the production of the hypercapsule. WcaJ as initiating enzyme of CPS biosynthesis, its presence determines the synthesis of capsule. Besides, different from rmpA, wcaJ sequence consistency is limited to the same serotype, which cause wcaJ functioning in different serotype strains with sequence recognition specificity.

Relationship Between Drug Resistance Characteristics and Biofilm Formation in Klebsiella Pneumoniae Strains

Objective

To conduct epidemiological analysis of Klebsiella pneumoniae (K. pneumoniae) with hypervirulence, and to investigate its drug resistance phenotype, Extended-spectrum β-lactamase (ESBLs) gene, virulence factor, capsular serotype and biofilm formation, so as to provide theoretical basis for further understanding of the drug resistance mechanism of K. pneumoniae with hypervirulence.

Methods

K. Pneumoniae were isolated from clinical samples collected from inpatients. All strains were identified by VITEK2 Compact using fully automatic microbial analyzer, the minimal inhibitory concentration (MIC) of antibiotics was determined by microbroth dilution test. The double disk diffusion method was used to detect the production of ESBLs, modified carbapenem inactivation method (mCIM) was used to detect the production of carbapenemase, and hypermucoviscosity phenotype was detected by wire drawing test. PCR was used to detect ESBLs gene, virulence factor and capsular serotype. Crystal violet staining was used to detect the ability of biofilm formation.

Results

The ESBLs genes detected in this study included strains blaTEM 35 (36.5%), blaSHV 51 (53.1%), and blaCTX-M 49 (51.0%). Most strains carried multiple ESBLs genes, but not all of them produce ESBLs. K1 and K2 accounted for 14.6% and 11.5% respectively. Most (91.7%) strains carried the fimH gene, and the other virulence genes were ybtS (53.1%), entB (46.9%), rmpA (41.7%), aerobactin (32.3%), allS (15.6%), kfu (15.6%). Of all the Klebsiella pneumoniae strains, 33 (34.4%) exhibited ESBLs phenotype, 16 (16.7%) were carbapenemase-producing, and 20 (20.8%) with ESBLs phenotype tested were resistant to all four drugs. The correlation between ESBLs-producing strains and biofilm formation was significantly increased compared to strains without ESBLs phenotype (P=0.035).

Conclusion

Compared to hypervirulent Klebsiella pneumoniae (hvKP), classical Klebsiella pneumoniae (cKP) has a tendency to acquire antibiotic resistance. Our study showed that genes encoding rmpA, K1 or K2, and kfu were highly associated with hvKP.

Hypervirulent Klebsiella pneumoniae Causing Neonatal Bloodstream Infections: Emergence of NDM-1-Producing Hypervirulent ST11-K2 and ST15-K54 Strains Possessing pLVPK-Associated Markers

Klebsiella pneumoniae is a major cause of neonatal sepsis. Hypervirulent Klebsiella pneumoniae (hvKP) that cause invasive infections and/or carbapenem-resistant hvKP (CR-hvKP) limit therapeutic options. Such strains causing neonatal sepsis have rarely been studied. Characterization of neonatal septicemic hvKP/CR-hvKP strains in terms of resistance and virulence was carried out. Antibiotic susceptibility, molecular characterization, evaluation of clonality, in vitro virulence, and transmissibility of carbapenemase genes were evaluated. Whole-genome sequencing (WGS) and mouse lethality assays were performed on strains harboring pLVPK-associated markers. About one-fourth (26%, 28/107) of the studied strains, leading to mortality in 39% (11/28) of the infected neonates, were categorized as hvKP. hvKP-K2 was the prevalent pathotype (64.2%, 18/28), but K54 and K57 were also identified. Most strains were clonally diverse belonging to 12 sequence types, of which ST14 was most common. Majority of hvKPs possessed virulence determinants, strong biofilm-forming, and high serum resistance ability. Nine hvKPs were carbapenem-resistant, harboring blaNDM-1/blaNDM-5 on conjugative plasmids of different replicon types. Two NDM-1-producing high-risk clones, ST11 and ST15, had pLVPK-associated markers (rmpA, rmpA2, iroBCDEN, iucABCDiutA, and peg-344), of which one co-transferred the markers along with blaNDM-1. The 2 strains revealed high inter-genomic resemblance with the other hvKP reference genomes, and were lethal in mouse model. To the best of our knowledge, this study is the first to report on the NDM-1-producing hvKP ST11-K2 and ST15-K54 strains causing fatal neonatal sepsis. The presence of pLVPK-associated markers and blaNDM-1 in high-risk clones, and the co-transmission of these genes via conjugation calls for surveillance of these strains. IMPORTANCE Klebsiella pneumoniae is a leading cause of sepsis in newborns and adults. Among the 2 major pathotypes of K. pneumoniae, classical (cKP) and hypervirulent (hvKP), hvKP causes community-acquired severe fatal invasive infections in even healthy individuals, as it possesses several virulence factors. The lack of comprehensive studies on neonatal septicemic hvKPs prompted this work. Nearly 26% diverse hvKP strains were recovered possessing several resistance and virulence determinants. The majority of them exhibited strong biofilm-forming and high serum resistance ability. Nine of these strains were also carbapenem (last-resort antibiotic)-resistant, of which 2 high-risk clones (ST11-K2 and ST15-K54) harbored markers (pLVPK) noted for their virulence, and were lethal in the mouse model. Genome-level characterization of the high-risk clones showed resemblance with the other hvKP reference genomes. The presence of transmissible carbapenem-resistant gene, blaNDM, along with pLVPK-markers calls for vigilance, as most clinical microbiology laboratories do not test for them.

Carbapenem-Resistant Klebsiella pneumoniae: Virulence Factors, Molecular Epidemiology and Latest Updates in Treatment Options

Klebsiella pneumoniae is a Gram-negative opportunistic pathogen responsible for a variety of community and hospital infections. Infections caused by carbapenem-resistant K. pneumoniae (CRKP) constitute a major threat for public health and are strongly associated with high rates of mortality, especially in immunocompromised and critically ill patients. Adhesive fimbriae, capsule, lipopolysaccharide (LPS), and siderophores or iron carriers constitute the main virulence factors which contribute to the pathogenicity of K. pneumoniae. Colistin and tigecycline constitute some of the last resorts for the treatment of CRKP infections. Carbapenemase production, especially K. pneumoniae carbapenemase (KPC) and metallo-β-lactamase (MBL), constitutes the basic molecular mechanism of CRKP emergence. Knowledge of the mechanism of CRKP appearance is crucial, as it can determine the selection of the most suitable antimicrobial agent among those most recently launched. Plazomicin, eravacycline, cefiderocol, temocillin, ceftolozane-tazobactam, imipenem-cilastatin/relebactam, meropenem-vaborbactam, ceftazidime-avibactam and aztreonam-avibactam constitute potent alternatives for treating CRKP infections. The aim of the current review is to highlight the virulence factors and molecular pathogenesis of CRKP and provide recent updates on the molecular epidemiology and antimicrobial treatment options.

Opposite evolution of pathogenicity driven by in vivo wzc and wcaJ mutations in ST11-KL64 carbapenem-resistant Klebsiella pneumoniae

AIMS

To investigate the in vivo evolution of the mucoid-phenotype of ST11-KL64 carbapenem-resistant Klebsiella pneumoniae (CRKP) isolated from the same patients and gain insights into diverse evolution and biology of these strains.

METHODS

Whole genome sequencing and bioinformatic analysis were used to determine the mutation involved in the mucoid phenotype of ST11-KL64 CRKP. Gene knockout, bacterial morphology and capsular polysaccharides (CPS) extraction were used to verify the role of wzc and wcaJ in the mucoid phenotypes. Antimicrobial susceptibility, growth assay, biofilm formation, host cell adhesion and virulence assay were used to investigate the pleiotropic role of CPS changes in ST11-KL64 CRKP strains.

RESULTS

Mutation of wzc S682N led to hypermucoid phenotype, which had negative impact on bacterial fitness and resulted in reduced biofilm formation and epithelial cell adhesion; while enhanced resistance to macrophage phagocytosis and virulence. Mutations of wcaJ gene led to non-mucoid phenotype with increased biofilm formation and epithelial cell adhesion, but reduced resistance of macrophage phagocytosis and virulence. Using virulence gene knockout, we demonstrated that CPS, rather than the pLVPK-like virulence plasmid, has a greater effect on mucoid phenotypic changes. CPS could be used as a surrogate marker of virulence in ST11-KL64 CRKP strains.

CONCLUSIONS

ST11-KL64 CRKP strains sacrifice certain advantages to develop pathogenicity by changing CPS with two opposite in vivo evolution strategies.

Characterization of Novel Bacteriophage vB_KpnP_ZX1 and Its Depolymerases with Therapeutic Potential for K57 Klebsiella pneumoniae Infection

A novel temperate phage vB_KpnP_ZX1 was isolated from hospital sewage samples using the clinically derived K57-type Klebsiella pneumoniae as a host. Phage vB_KpnP_ZX1, encoding three lysogen genes, the repressor, anti-repressor, and integrase, is the fourth phage of the genus Uetakevirus, family Podoviridae, ever discovered. Phage vB_KpnP_ZX1 did not show ideal bactericidal effect on K. pneumoniae 111-2, but TEM showed that the depolymerase Dep_ZX1 encoded on the short tail fiber protein has efficient capsule degradation activity. In vitro antibacterial results show that purified recombinant Dep_ZX1 can significantly prevent the formation of biofilm, degrade the formed biofilm, and improve the sensitivity of the bacteria in the biofilm to the antibiotics kanamycin, gentamicin, and streptomycin. Furthermore, the results of animal experiments show that 50 µg Dep_ZX1 can protect all K. pneumoniae 111-2-infected mice from death, whereas the control mice infected with the same dose of K. pneumoniae 111-2 all died. The degradation activity of Dep_ZX1 on capsular polysaccharide makes the bacteria weaken their resistance to immune cells, such as complement-mediated serum killing and phagocytosis, which are the key factors for its therapeutic action. In conclusion, Dep_ZX1 is a promising anti-virulence agent for the K57-type K. pneumoniae infection or biofilm diseases.

The Epidemiology of Invasive, Multipleantibiotic-resistant Klebsiella pneumoniae Infection in a Breeding Colony of Immunocompromised NSG Mice

Klebsiella pneumoniae (Kp) is a gram-negative opportunistic pathogen that causes severe pneumonia, pyelonephritis, and sepsis in immunocompromised hosts. During a 4-mo interval, several NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) breeders and pups in our facilities were diagnosed with Kp infections. An initial 6 adult and 1 juvenile NSG mice were submitted for necropsy and histologic examination because of acute onset of diarrhea and death. The evaluation revealed typhlocolitis in 2 of the mice and tritrichomoniasis in all 7. Escherichia coli positive for polyketide synthase (pks+) and Kp were isolated from the intestines. Given a history of sepsis due to pks+ E. coli in NSG mice in our facilities and determination of its antimicrobial susceptibility, trimethoprim-sulfamethoxazole (TMP-SMX) was administered to the colony in the drinking water for 4 wk. After this intervention, an additional 21 mice became ill or died; 11 of these mice had suppurative pneumonia, meningoencephalitis, hepatitis, metritis, pyelonephritis, or sepsis. Kp was cultured from pulmonary abscesses or blood of 10 of the mice. Whole-genome sequencing (WGS) indicated that the Kp isolates contained genes associated with phenotypes found in pore-forming Kp isolates cultured from humans with ulcerative colitis and primary sclerosing cholangitis. None of the Kp isolates exhibited a hyperviscous phenotype, but 13 of 14 were resistant to TMP-SMX. Antimicrobial susceptibility testing indicated sensitivity of the Kp to enrofloxacin, which was administered in the drinking water. Antibiotic sensitivity profiles were confirmed by WGS of the Kp strains; key virulence and resistance genes to quaternary ammonia compounds were also identified. Enrofloxacin treatment resulted in a marked reduction in mortality, and the study using the NSG mice was completed successfully. Our findings implicate intestinal translocation of Kp as the cause of pneumonia and systemic infections in NSG mice and highlight the importance of identification of enteric microbial pathogens and targeted antibiotic selection when treating bacterial infections in immunocompromised mice.

Capsule type defines the capability of Klebsiella pneumoniae in evading Kupffer cell capture in the liver

Polysaccharide capsule is the main virulence factor of K. pneumoniae, a major pathogen of bloodstream infections in humans. While more than 80 capsular serotypes have been identified in K. pneumoniae, only several serotypes are frequently identified in invasive infections. It is documented that the capsule enhances bacterial resistance to phagocytosis, antimicrobial peptides and complement deposition under in vitro conditions. However, the precise role of the capsule in the process of K. pneumoniae bloodstream infections remains to be elucidated. Here we show that the capsule promotes K. pneumoniae survival in the bloodstream by protecting bacteria from being captured by liver resident macrophage Kupffer cells (KCs). Our real-time in vivo imaging revealed that blood-borne acapsular K. pneumoniae mutant is rapidly captured and killed by KCs in the liver sinusoids of mice, whereas, to various extents, encapsulated strains bypass the anti-bacterial machinery in a serotype-dependent manner. Using capsule switched strains, we show that certain high-virulence (HV) capsular serotypes completely block KC’s capture, whereas the low-virulence (LV) counterparts confer partial protection against KC’s capture. Moreover, KC’s capture of the LV K. pneumoniae could be in vivo neutralized by free capsular polysaccharides of homologous but not heterologous serotypes, indicating that KCs specifically recognize the LV capsules. Finally, immunization with inactivated K. pneumoniae enables KCs to capture the HV K. pneumoniae. Together, our findings have uncovered that KCs are the major target cells of K. pneumoniae capsule to promote bacterial survival and virulence, which can be reversed by vaccination.

Klebsiella pneumoniae is a major human pathogen. While capsule is the main virulence factor of the pathogen, only several of more than 80 capsule serotypes are frequently identified in invasive infections. However, it remains unclear how capsule contributes to K. pneumoniae virulence. Here we show that capsule type defines K. pneumoniae virulence by differential escape of immune surveillance in the liver. While low-virulence (LV) types are captured by Kupffer cells (KCs), high-virulence (HV) types circumvent the anti-bacterial machinery. Further, inactivated K. pneumoniae vaccine enables KCs to capture the HV K. pneumoniae and protects mice from lethal infection. Our findings explain the clinical prevalence of HV capsule types, and provide promising insights for future vaccine development.

Establishing a Klebsiella pneumoniae-Based Cell-Free Protein Synthesis System

Cell-free protein synthesis (CFPS) systems are emerging as powerful platforms for in vitro protein production, which leads to the development of new CFPS systems for different applications. To expand the current CFPS toolkit, here we develop a novel CFPS system derived from a chassis microorganism Klebsiella pneumoniae, an important industrial host for heterologous protein expression and the production of many useful chemicals. First, we engineered the K. pneumoniae strain by deleting a capsule formation-associated wzy gene. This capsule-deficient strain enabled easy collection of the cell biomass for preparing cell extracts. Then, we optimized the procedure of cell extract preparation and the reaction conditions for CFPS. Finally, the optimized CFPS system was able to synthesize a reporter protein (superfolder green fluorescent protein, sfGFP) with a maximum yield of 253 ± 15.79 μg/mL. Looking forward, our K. pneumoniae-based CFPS system will not only expand the toolkit for protein synthesis, but also provide a new platform for constructing in vitro metabolic pathways for the synthesis of high-value chemicals.

Genomic surveillance for multidrug-resistant or hypervirulent Klebsiella pneumoniae among United States bloodstream isolates

BACKGROUND

Klebsiella pneumoniae strains have been divided into two major categories: classical K. pneumoniae, which are frequently multidrug-resistant and cause hospital-acquired infections in patients with impaired defenses, and hypervirulent K. pneumoniae, which cause severe community-acquired and disseminated infections in normal hosts. Both types of infections may lead to bacteremia and are associated with significant morbidity and mortality. The relative burden of these two types of K. pneumoniae among bloodstream isolates within the United States is not well understood.

METHODS

We evaluated consecutive K. pneumoniae isolates cultured from the blood of hospitalized patients at Northwestern Memorial Hospital (NMH) in Chicago, Illinois between April 2015 and April 2017. Bloodstream isolates underwent whole genome sequencing, and sequence types (STs), capsule loci (KLs), virulence genes, and antimicrobial resistance genes were identified in the genomes using the bioinformatic tools Kleborate and Kaptive. Patient demographic, comorbidity, and infection information, as well as the phenotypic antimicrobial resistance of the isolates were extracted from the electronic health record. Candidate hypervirulent isolates were tested in a murine model of pneumonia, and their plasmids were characterized using long-read sequencing. We also extracted STs, KLs, and virulence and antimicrobial resistance genes from the genomes of bloodstream isolates submitted from 33 United States institutions between 2007 and 2021 to the National Center for Biotechnology Information (NCBI) database.

RESULTS

Consecutive K. pneumoniae bloodstream isolates (n = 104, one per patient) from NMH consisted of 75 distinct STs and 51 unique capsule loci. The majority of these isolates (n = 58, 55.8%) were susceptible to all tested antibiotics except ampicillin, but 17 (16.3%) were multidrug-resistant. A total of 32 (30.8%) of these isolates were STs of known high-risk clones, including ST258 and ST45. In particular, 18 (17.3%) were resistant to ceftriaxone (of which 17 harbored extended-spectrum beta-lactamase genes) and 9 (8.7%) were resistant to meropenem (all of which harbored a carbapenemase genes). Four (3.8%) of the 104 isolates were hypervirulent K. pneumoniae, as evidenced by hypermucoviscous phenotypes, high levels of virulence in a murine model of pneumonia, and the presence of large plasmids similar to characterized hypervirulence plasmids. These isolates were cultured from patients who had not recently traveled to Asia. Two of these hypervirulent isolates belonged to the well characterized ST23 lineage and one to the re-emerging ST66 lineage. Of particular concern, two of these isolates contained plasmids with tra conjugation loci suggesting the potential for transmission. We also analyzed 963 publicly available genomes of K. pneumoniae bloodstream isolates from locations within the United States. Of these, 465 (48.3%) and 760 (78.9%) contained extended-spectrum beta-lactamase genes or carbapenemase genes, respectively, suggesting a bias towards submission of antibiotic-resistant isolates. The known multidrug-resistant high-risk clones ST258 and ST307 were the predominant sequence types. A total of 32 (3.3%) of these isolates contained aerobactin biosynthesis genes and 26 (2.7%) contained at least two genetic features of hvKP strains, suggesting elevated levels of virulence. We identified 6 (0.6%) isolates that were STs associated with hvKP: ST23 (n = 4), ST380 (n = 1), and ST65 (n = 1).

CONCLUSIONS

Examination of consecutive isolates from a single center demonstrated that multidrug-resistant high-risk clones are indeed common, but a small number of hypervirulent K. pneumoniae isolates were also observed in patients with no recent travel history to Asia, suggesting that these isolates are undergoing community spread in the United States. A larger collection of publicly available bloodstream isolate genomes also suggested that hypervirulent K. pneumoniae strains are present but rare in the USA; however, this collection appears to be heavily biased towards highly antibiotic-resistant isolates (and correspondingly away from hypervirulent isolates).

Unusual Hypermucoviscous Clinical Isolate of Klebsiella pneumoniae with No Known Determinants of Hypermucoviscosity

Klebsiella pneumoniae can be broadly classified into classical strains that cause drug-resistant, hospital-associated infections and hypervirulent strains that cause invasive, community-acquired, drug-susceptible infections. Hypermucoviscosity in Klebsiella pneumoniae has been associated with immune evasion and hypervirulence. A string-test-positive, hypermucoviscous strain of Klebsiella pneumoniae, P34, was isolated from the cystic lesion of a patient who reported to a tertiary care hospital in Jodhpur, Rajasthan, India. Given the antibiotic-susceptible and hypermucoviscous nature of the isolate, it was suspected to belong to the hypervirulent lineage of Klebsiella pneumoniae. However, P34 did not overproduce capsular polysaccharides and also remained susceptible to the antimicrobial effects of human serum when tested alongside strains that were non-hypermucoviscous. Sequencing of the genome of P34 revealed the absence of any large virulence plasmids or integrative conjugative elements that usually carry hypermucoviscosity- and hypervirulence-associated genes. P34 also lacked key virulence determinants such as aerobactin, yersiniabactin, and salmochelin biosynthesis clusters. In addition, P34 lacked homologs for genes associated with enhanced capsule synthesis and hypermucoviscosity, such as rmpA, rmpA2, rmpC, and rmpD (regulator of mucoid phenotype). These observations suggest that P34 may harbor novel genetic determinants of hypermucoviscosity independent of the indirectly acting rmpA and the recently described rmpD. IMPORTANCE Hypermucoviscosity is a characteristic of hypervirulent Klebsiella pneumoniae strains, which are capable of causing invasive disease in community settings. This study reports phenotyping and genomic analysis of an unusual clinical isolate of Klebsiella pneumoniae, P34, which exhibits hypermucoviscosity and yet does not harbor rmp (regulator of mucoid phenotype) genes, which are known determinants of hypermucoviscosity (rmpA and rmpD). Similar clinical isolates belonging to the K. pneumoniae complex that are hypermucoviscous but do not harbor the rmp loci have been reported from India and abroad, indicating the prevalence of unknown determinants contributing to hypermucoviscosity. Therefore, strains like P34 will serve as model systems to mechanistically study potentially novel determinants of hypermucoviscosity in the K. pneumoniae complex.

Genomic epidemiology and temperature dependency of hypermucoviscous Klebsiella pneumoniae in Japan

Klebsiella pneumoniae (Kp) has emerged as a global life-threatening pathogen owing to its multidrug resistance and hypervirulence phenotype. Several fatal outbreaks of carbapenem-resistant hypervirulent Kp have been reported recently. Hypermucoviscosity (HMV) is a phenotype commonly associated with hypervirulence of Kp, which is usually regulated by rmpA or rmpA2 (regulators of the mucoid phenotype). Here, we found that temperature was important in the HMV phenotype of Kp, and the impact of temperature on HMV was not uniform among strains. We investigated the HMV phenotype at 37 °C and room temperature (20–25 °C) in 170 clinically isolated hypermucoviscous Kp strains in Japan and analysed the association between the HMV phenotype, virulence genes and antimicrobial resistance (AMR) genes. String length distribution at different temperatures was correlated with the genomic population of Kp. The strains carrying rmpA/rmpA2 frequently showed the HMV phenotype at 37 °C, while the strains negative for these genes tended to show the HMV phenotype at room temperature. Hypervirulent Kp clusters carrying rmpA/rmpA2 without extended-spectrum beta-lactamases (ESBL)/carbapenemases produced higher string lengths at 37 °C than at room temperature, and were mostly isolated from the respiratory tract. Other HMV strains showed distinct characteristics of not carrying rmpA/rmpA2 but were positive for ESBL/carbapenemases, with a higher string length at room temperature than at 37 °C, and were frequently isolated from bloodstream infections. In total, 21 (13.5 %) HMV isolates carried ESBL and carbapenemases, among which five isolates were carbapenem-resistant hypervirulent Kp with a pLVPK-like plasmid (an epidemic virulence plasmid) and a pKPI-6-like plasmid (an epidemic bla_IMP-6-bearing plasmid in Japan), suggesting the convergence of worldwide hypervirulence and epidemic AMR in Japan.

Whole Genome Characterization of the High-Risk Clone ST383 Klebsiella pneumoniae with a Simultaneous Carriage of blaCTX-M-14 on IncL/M Plasmid and blaCTX-M-15 on Convergent IncHI1B/IncFIB Plasmid from Egypt

Recently, Egypt has witnessed the emergence of multidrug-resistant (MDR) Klebsiella pneumoniae, which has posed a serious healthcare challenge. The accelerated dissemination of blaCTX-M genes among these MDR K. pneumoniae, particularly blaCTX-M-14 and blaCTX-M-15, have been noted. In this study, we investigated the occurrence of blaCTX-M-IV among K. pneumoniae recovered from the laboratory of a major hospital in Alexandria. The 23 tested isolates showed an MDR phenotype and the blaCTX-M-IV gene was detected in ≈22% of the isolates. The transformation of plasmids harboring blaCTX-M-IV to chemically competent cells of Escherichia coli DH5α was successful in three out of five of the tested blaCTX-M-IV-positive isolates. Whole genome sequencing of K22 indicated that the isolate belonged to the high-risk clone ST383, showing a simultaneous carriage of blaCTX-M-14 on IncL/M plasmid, i.e., pEGY22_CTX-M-14, and blaCTX-M-15 on a hybrid IncHI1B/IncFIB plasmid, pEGY22_CTX-M-15. Alignment of both plasmids revealed high similarity with those originating in the UK, Germany, Australia, Russia, China, Saudi Arabia, and Morocco. pEGY22_CTX-M-15 was a mosaic plasmid that demonstrated convergence of MDR and virulence genes. The emergence of such a plasmid with enhanced genetic plasticity constitutes the perfect path for the evolution of K. pneumoniae isolates causing invasive untreatable infections especially in a country with a high burden of infectious diseases such as Egypt. Therefore there is an imperative need for countrywide surveillances to monitor the prevalence of these superbugs with limited therapeutic options.

Three Novel Sequence Types Carbapenem-Resistant Klebsiella pneumoniae Strains ST5365, ST5587, ST5647 Isolated from Two Tertiary Teaching General Hospitals in Shanxi Province, in North China: Molecular Characteristics, Resistance and Virulence Factors

Background

Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a significant threat to public health and has already drawn worldwide attention. Hence, we aim to comprehensively analyze the case condition, as well as molecular epidemiology, resistance and virulence of three CRKP isolates with new sequence types (STs).

Methods

Three CRKP were collected from November 2019 to April 2021. The three patients’ clinical characteristics were analyzed through His system. In order to screen phenotype of metallo-carbapenemase, the modified Carbapenem Inactivation Method (mCIM) and EDTA-modified Carbapenem Inactivation Method (eCIM) were conducted. Three isolates were subjected to antimicrobial susceptibility testing (AST) using the agar dilution method or minimal broth dilution method. The string test, the sedimentation assay, biofilm formation and the serum resistance assay were performed as phenotypic experiments to assist in evaluating virulence. The presence of resistance and virulence genes were detected by Whole-Genome Sequencing (WGS). Serotypes and new STs were compared and determined by multi-locus sequence typing (MLST).

Results

Overall, all Klebsiella pneumoniae isolates were multi-resistant, but sensitive to tigecycline and colistin. Among them, all formed biofilms, strain 1 and strain 2 were classified as moderate-producers, while strain 3 as weak-producer. The results of the serum resistance assay indicated that only strain 2 was resistant. From WGS analysis, it showed that all isolates co-harbored multiple resistance genes, such as carbapenemase genes, sulfonamides, fluoroquinolones, aminoglycosides, and tetracyclines. Meanwhile, several virulence genes were also contained, including siderophores, fimbriae, capsule and lipopolysaccharides-associated genes. The serotypes of strain 1 and strain 2 manifested K35 and KL47, respectively.

Conclusion

Three novel ST5365, ST5587, ST5647 were first discovered in North China. Our study suggested that we should pay more attention to their resistance. And the results will help treat CRKP infections caused by these novel STs.

Multidrug-resistant Klebsiella pneumoniae: a retrospective study in Manaus, Brazil

Klebsiella pneumoniae is an opportunistic pathogen that can cause several infections, mainly in hospitalised or immunocompromised individuals. The spread of K. pneumoniae emerging virulent and multidrug-resistant clones is a worldwide concern and its identification is crucial to control these strains especially in hospitals. This article reports data related to multi-resistant K. pneumoniae strains, isolated from inpatients in the city of Manaus, Brazil, harbouring virulence and antimicrobial-resistance genes, including high-risk international clones belonging to clonal group (CG) 258. Twenty-one strains isolated from different patients admitted to four hospitals in the city of Manaus, located in the state of Amazonas, Northern Brazil (Amazon Rainforest region) were evaluated. The majority of strains (61.9% n = 13) were classified as multidrug-resistant (MDR), and five strains (23.8%) as extensively drug-resistant (XDR). Several virulence and antimicrobial-resistance genes were found among the strains and eight strains (38.1%) presented the hyper-mucoviscous phenotype. MLST analysis demonstrated a great diversity of STs among the strains, totaling 12 different STs (ST11, ST23, ST198, ST277, ST307, ST340, ST378, ST462, ST502, ST3991, ST3993 and ST5209). Three of these (ST11, ST23 and ST340) belong to CG258.

Molecular Epidemiology of Hypervirulent K. pneumoniae and Problems of Health-Care Associated Infections

The review describes virulence factors of hypervirulent K. pneumoniae (hvKp) including genes determining its virulence and discusses their role in the development of health-care associated infections. The contribution of individual virulence factors and their combination to the development of the hypervirulence and the prospects of using these factors as biomarkers and therapeutic targets are described. Virulence factors of hvKp and "classical" K. pneumoniae strains (cKp) with no hypervirulence genes were compared. The mechanisms of biofilm formation by hvKp and high incidence of its antibiotic resistance are of particular importance for in health care institutions. Therefore, the development of methods for hvKp identification allowing early prevention of severe hvKp infection and novel approaches to abrogate its spreading are new challenges for epidemiology, infection diseases, and critical care medicine. New technologies including bacteriological and molecular studies make it possible to develop innovative strategies to diagnose and treat infection caused by hvKp. These include monitoring of both genetic biomarkers of hvKp and resistance plasmid that carry of virulence genes and antibiotic resistance genes, creation of immunological agents for the prevention and therapy of hvKp (vaccines, monoclonal antibodies) as well as personalized hvKp-specific phage therapies and pharmaceuticals enhancing the effect of antibiotics. A variety of approaches can reliably prepare our medicine for a new challenge: spreading of life-threatening health-care associated infections caused by antibiotic-resistant hvKp strains.

The Epidemiology, Virulence and Antimicrobial Resistance of Invasive Klebsiella pneumoniae at a Children's Medical Center in Eastern China

Objective

This study investigated the epidemiology, virulence and drug resistance of invasive Klebsiella pneumoniae (K. pneumoniae) isolates at a children’s medical center in eastern China in order to obtain epidemiologic, virulence, and antimicrobial resistance data that can guide for the selection and development of anti-infection treatments.

Methods

A total of 94 invasive K. pneumoniae strains were isolated from children between January 2016 and December 2020 at the Children’s Hospital of Soochow University. The strains were identified by mass spectrometry. The Kirby–Bauer method and VITEK 2 Compact system were used to analyze the antimicrobial susceptibility. Polymerase chain reaction (PCR) and sequencing was performed to detect the capsular serotypes, virulence-associated genes, β-lactam antibiotic resistance genes and multilocus sequence typing.

Results

The PCR results showed that 87 strains (92.55%) of invasive K. pneumoniae were hypervirulent capsular serotypes, with K57 as the dominant capsular serotype (62.77%). All strains carried virulence-associated genes. Among them, 84 strains (89.36%) carried hypervirulence genes, with iroB (86.17%) being the predominant; meanwhile, other virulence genes, including wabG (100.00%), mrkD (98.94%), ycfM (96.81%), fimH (95.74%) and Uge (88.30%), were detected in most strains. All strains carried β-lactam antibiotic resistance genes; the main extended-spectrum β-lactamase gene was bla_SHV-11 (86.17%) and the major AmpC cephalosporinase genes were bla_FOX-1 (86.17%) and bla_ACT-1 (70.21%). Carbapenemase genes were detected in only a few isolates. Notably, 12 invasive K. pneumoniae isolates were identified as carbapenem-resistant and hypervirulent K. pneumoniae (CR-HVKP), and 14 other multidrug resistance (MDR) isolates were also detected.

Conclusion

The results of this study reveal the epidemiology, virulence and antimicrobial resistance of invasive K. pneumoniae in pediatric patients. Both CR-HVKP and MDR strains were identified, which should be of great concern to clinicians.